As disclosed in Patent Literatures 1 and 2, Li2O—Al2O3—SiO2 based crystallized glass obtained by precipitating LAS-based crystals (β-quartz solid solution or β-spodumene solid solution) as main crystals is conventionally used as a material for front windows of oil stoves, wood stoves and the like, substrates for high-technology products, such as color filter substrates, image sensor substrates and the like, setters for firing electronic components, microwave oven shelfs, electromagnetic induction heating cooker top plates and fire proof windows.
Li2O—Al2O3—SiO2-based crystallized glass has low coefficient of thermal expansion and high mechanical strength, and therefore has excellent thermal properties. Furthermore, the glass can change the crystal species to be precipitated by changing the heat treatment conditions in the crystallization step. Therefore, both of transparent crystallized glass (containing β-quartz solid solution precipitated therein) and white opaque crystallized glass (containing β-spodumene solid solution precipitated therein) can be produced from a mother glass of the same composition and selectively applied to as usage.
Such crystallized glass can be generally produced by forming Li2O—Al2O3—SiO2-based crystallizable glass containing a nucleation agent, such as TiO2 or ZrO2, into a desired shape by a pressing process or a roll-out process, then subjecting the formed product to heat treatment at temperatures of about 600° C. to 800° C. to form crystal nuclei and then further subjecting the product to heat treatment at temperatures of about 800° C. to 1100° C. to precipitate LAS-based crystals therein.
Particularly, crystallized glass in sheet form can be produced by forming molten glass into a sheet by a roll-out process in which molten glass is guided and sandwiched between a pair of forming rolls and rolled while being quenched by the rolls, and then subjecting the formed product to heat treatment to crystallize it.
However, if crystallized glass in sheet form is produced using a roll-out process, the width of the forming rolls must be large and the deformation of the forming rolls at high temperatures is therefore significant. This presents a problem in that it is difficult to stably form sheet glass large in the width direction of the forming rolls. In addition, since the molten glass must be quenched by the forming rolls, a problem also arises in that the production speed cannot be increased.
To solve these problems, a float process is proposed in Patent Literatures 3 and 4, i.e., a process for obtaining crystallized glass in sheet form by floating molten glass on a bath of molten metal tin (float bath) to form the molten glass into a sheet and then subjecting the sheet glass to heat treatment to crystallize it.